Acquisition and Disposition (Details) - USD ($) $ in Thousands		6 Months Ended		9 Months Ended
	Mar. 16, 2015	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Mar. 16, 2015	Dec. 31, 2014
Recognized amounts of tangible assets and liabilities:
Goodwill (including deferred tax adjustment of $2,298)						$ 218,972		$ 398,164
Sale of business
Loss on sale				$ 9,501	$ 0
3Q Digital Inc
Acquisition and Disposition
Estimate of potential undiscounted future contingent consideration payments, low end of range							$ 0
Estimate of potential undiscounted future contingent consideration payments, high end of range							35,000
Total consideration
Cash consideration per purchase agreement	$ 30,245
Estimated fair value of contingent consideration	17,940	$ 17,940					17,940
Recognized amounts of tangible assets and liabilities:
Current assets							4,135
Property and equipment							164
Other assets							389
Current liabilities							(822)
Total tangible assets and liabilities:							3,866
Identifiable intangible assets							4,773
Goodwill (including deferred tax adjustment of $2,298)							41,845
Total							50,484
Deferred tax adjustment							2,298
Reconciliation of accrued earnout consideration
Contingent consideration at acquisition date		17,940
September 30, 2015	$ 17,940
3Q Digital Inc | Customer relationships
Recognized amounts of tangible assets and liabilities:
Identifiable intangible assets							4,300
Amortization period	7 years
3Q Digital Inc | Tradenames and trademarks
Recognized amounts of tangible assets and liabilities:
Identifiable intangible assets							300
Amortization period	2 years
3Q Digital Inc | Non-compete agreements
Recognized amounts of tangible assets and liabilities:
Identifiable intangible assets							200
Amortization period	3 years
3Q Digital Inc | Level 3 | Contingent Consideration
Total consideration
Estimated fair value of contingent consideration	$ 17,940	19,539	$ 19,539	19,539		$ 19,539	17,940
Reconciliation of accrued earnout consideration
Contingent consideration at acquisition date		17,940
Accretion of interest		1,599
September 30, 2015	$ 17,940	$ 19,539	19,539	$ 19,539
B2B research business
Sale of business
Loss on sale			$ 9,501
B2B research business | Maximum
Sale of business
Percent of total Company revenue (less than)			5.00%
Portion at Fair Value Measurement [Member] | 3Q Digital Inc | Customer relationships
Recognized amounts of tangible assets and liabilities:
Identifiable intangible assets and goodwill							$ 48,185